Russian opposition leader Alexei Navalny has called for protests across Russia on January 28 to support a boycott of the country's upcoming presidential election.

Navalny appealed for the protests on Wednesday, the same day President Vladimir Putin formally registered for a re-election bid.

Polls show that Putin is likely to win another six-year term when the election is held on March 18.

Navalny has been barred from the election because of a suspended prison sentence he says was fabricated. He contends that Putin, who has spent the last 17 years as either president or prime minister, has been in power too long. Navalny says Putin's popularity is largely due to biased state media and an electoral system that excludes legitimate opponents.

Putin, a former KGB officer, is running as an independent, a decision some observers believe would enhance his image as a leader of a nation instead of a party political figure.

Allies have praised Putin for restoring national pride and enhancing Russia's position as a global leader with military interventions in Syria and Ukraine.